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Remove parity branches from arm_sqrt_q15 #339

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Remove parity branches from arm_sqrt_q15 #339

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21 changes: 5 additions & 16 deletions Source/FastMathFunctions/arm_sqrt_q15.c
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Original file line number Diff line number Diff line change
Expand Up @@ -65,15 +65,11 @@ ARM_DSP_ATTRIBUTE arm_status arm_sqrt_q15(
{
signBits1 = __CLZ(number) - 17;

/* Force an even normalization shift. */
signBits1 &= ~1;

/* Shift by the number of signBits1 */
if ((signBits1 % 2) == 0)
{
number = number << signBits1;
}
else
{
number = number << (signBits1 - 1);
}
number = number << signBits1;
/* Start value for 1/sqrt(x) for the Newton iteration */
var1 = sqrt_initial_lut_q15[(number>> 11) - (Q12QUARTER >> 11)];

Expand All @@ -100,14 +96,7 @@ ARM_DSP_ATTRIBUTE arm_status arm_sqrt_q15(
var1 = ((q15_t) (((q31_t) number * var1) >> 12));

/* Shift the output down accordingly */
if ((signBits1 % 2) == 0)
{
var1 = var1 >> (signBits1 / 2);
}
else
{
var1 = var1 >> ((signBits1 - 1) / 2);
}
var1 = var1 >> (signBits1 / 2);
*pOut = var1;


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